Bug

In src/ethereum/forks/prague/vm/precompiled_contracts/bls12_381/__init__.py, both scalar pair decoders construct an InvalidParameter exception but never raise it:

def decode_g1_scalar_pair(data: Bytes) -> Tuple[Point3D[FQ], int]:
    if len(data) != 160:
        InvalidParameter("Input should be 160 bytes long")  # should be: raise InvalidParameter(...)
    ...

def decode_g2_scalar_pair(data: Bytes) -> Tuple[Point3D[FQ2], int]:
    if len(data) != 288:
        InvalidParameter("Input should be 288 bytes long")  # should be: raise InvalidParameter(...)
    ...

Python silently discards the constructed object. The length guard is a no-op.

Why it hasn't caused issues

The current callers (bls12_g1_msm, bls12_g2_msm) always validate len(data) % LENGTH_PER_PAIR != 0 before looping, and pass exact-length slices to the decoders. So the guard is currently unreachable. But it creates a false contract: anyone calling these functions directly (tests, tooling, forks) would receive no protection.

Fix

Add raise to both guards.